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Dear Zcuc,
Tomus of the old books, or volumes may carry different dates of publication. But a single volume may compose of several fascicules; they may also different dates of publication. Sometimes dates of publication were not mentioned there. Under such circumstance, authors search the exact date of publications in various ways. Results of such researches are published separately in some bibliographical journals.
Have you an example that you have hesitation on the date of publication?